The perfluoronated ionomer NafionŽ has been investigated as a surface for medical microsensor implants since the early 1990s largely due to its biocompatibility and selective permability. One method for assessing the ability of surfaces to reduce inflammatory response is by use of 3-morpholinosydnonimine N-ethylcarbamide (SIN-1) that gradually decomposes in the presence of

O₂ to form NO and the superoxide ion in PBS buffer. As these two reactive molecules form, they quickly combine to form peroxynitrite, known to play a key role in the biochemistry of inflammation. Adding 4-hydroxyphenylacetic acid (4-HPA) to a solution of SIN-1 results in rapid nitration to form NO₂HPA by way of the peroxynitrite thus formed. This product is easily quantified by its UV spectrum. Use of these reagents with other biocompatible surfaces based on TiO₂ has previously been a useful approach to identify the role of these surfaces in catalytic decomposition of peroxynitrite. Simple and modified NafionŽ films have now shown similar reduction of the nitration of 4-HPA in the presence of SIN-1. Details of the role of the NafionŽ surface in preventing this reaction, and therefore a possible mechanism for its biocompatibility will be presented.